This invention is directed to the field of blenders, and more particular, to blenders adapted for mixing polymers with sludge.
Various mixing devices have long been utilized for mixing polymeric flocculants to improve their contact with a low solids mixture. A water based slurry containing solids from which the water is to be removed is a common situation which presents itself in many industries. Many techniques have been utilized in handling such slurries (whether sludges or whether having other physical properties) for enhancing water removal, such as improved centrifugation or filtration, including vacuum filtration. In many of such water removal process techniques, the dewatering can be even further enhanced via the addition of a suitable polymeric substance. Suitable polymeric substances vary widely, depending upon the substance to be dewatered and its chemical, physical, and electrostatic properties. In many sludge handling applications a suitable polymer might be a high molecular weight and high charge density cationic polymer. However, in many commonly encountered applications, such as in the treatment of sewage sludge, achieving enhanced water removal even with addition of a suitably selected polymer is often difficult to achieve. One approach often used, which is rather expensive, is simply to increase the polymer dosage. However, in some cases, even that technique does not provide much improvement. In such cases, the ultimate solids dryness remains sufficiently low that significant savings in further handling costs (particularly with respect to charges for drying, transportation, and disposal) could be achieved if only the polymer addition achieved the performance results in full scale that were (and sometimes still are) seen in comparable bench scale trials.
A common problem encountered in the methods heretofore tried which are of interest to us is that polymer addition is often done only in conjunction with pumps designed to move the material. In such cases, the amount of work done on both the sludge and to the polymer being added has been primarily (if not totally) dependent on the work that the pump device, such as a progressive cavity pump impeller, did in the process of moving the sludge or slurry from one location to another. Thus, those methods inevitably leave the results in the hands of the selection of a few variables, namely polymer selection and dosage rate, since the pump itself is usually provided for a fixed service (i.e., flow, impeller rpm, and pressure differential). It is often rather difficult (if not impossible) to accomplish a quick adjustment of the pump, so, plant workmen are often found to be simply too lazy or too pressed for time to properly make use of the available adjustments, if any. So, a commonly encountered situation is that vendors of polymers are called in to test their various products, at different dosages, until an optimum product and dosage selection are attained to most cost effectively achieve the desired dewatering results.
Thus, there remains a continuing and as yet unmet need for a device that would provide immediate and precise control over polymer mixing, and which separates the work of sludge/polymer mixing from sludge pumping, and which can withstand the hazards inherent in sludges from sources such as municipal wastewater treatment plant operations.